The problem with time machines, is when they start.

Only one I would trust with the power to remake the future as he saw fit.....

And they crucified him (literaly).

There is no absolute cartesian spacial coordinates. These are conventions we make for ourselves. The choice of "zero-zero-zero" for the X,Y, and Z coordinates is arbitrary and all other positions are relative to that first arbitrary choice.

We are all floating in a sea of ambiguity when it comes to 'position'.

I agree with "There is no absolute cartesian spacial coordinates", but that still does not change the fact that had I somehow dropped a marker in in space in 1986 and I am somehow able to travel backward in time 20 years, that the marker would not be present.

Most of us still view Space-Time-Matter from the viewpoint of the Copernican Model (spelling?) and your viewpoint has credence under that model . . .

However the best understanding of Space-Time-Matter has advanced quite a lot since then with Newton, Einstein and Hawking leading us through Newtonian physics, reactivity, and quantum mechanics.

We can no longer think of space as an empty table-top which the items in the universe roll around upon.

There is no pervasive medium within which you can anchor such a 'dropped marker'. The 'Aether' does not exist.

Remember the old TV show "The Time Tunnel" while its pretty silly now, they did have one interesting concept that might work. The Tunnel

First you make a wormhole. (not as far fetched as we think, we are making very small ammounts of negative energy already) the wormhole is maintained for ever and links the two points in space.

Now you have one end, and a friend has the other. They board a fast as light ship (or almost as fast), and you remain on earth, For each of you time passes differently, but at the same time the wormholes keep the time and spaces linked. (BOTH WORMHOLES ARE MOVING FORWARD IN TIME, JUST AT DIFFERENT RATES) the differential between the 2 wormholes now allows you to step from one to another and links 2 points not only different in space but also in time.

And with this tunnel you arrive at a safe place, unless your friend has died and someone placed on end in an unsafe place.

Now you have a time tunnel if they are in the same place, or a time and space tunnel if they have moved.

Of course this goes beyond what we can do now, and what we might one day be able to do, but again, you cannot go further back in time that the moment that the wormhole is created.

Which brings us back to Molly's original question, why are we not seeing time visitors? Maybe because they cant come this far back to such a primative time.

But we might in the future meet such people who have travelled from the more distant future. In which case we will need some better words to explain our concepts of past-present and future.

But that's a problem for a future scholar to work on.

Really, great post. I liked your summary and your conclusions.

I just have one small problem with your #3... It presumes determinism. The greatest minds in physics have rejected the ability to predict the behaviour of particles. With the coming of Quantum Mechanics and Chaos Theory we now realize that the nature of the universe makes it such that cause-and-effect can only be used to predict/control future events on a very limited basis.

The more time goes by the less and less foreknowledge/control we have of future events.

Yes, I'm saying that with enough information, you could predict. Now, I'm also saying that it is a terribly large amount of information. I will grant that it is easier to reverse than to predict since you only have to observe and record all the information, but not have to know how it happened.

I do not understand your last statement that "The more time goes by the less and less foreknowledge/control we have of future events". Of course, although we might not be able to predict the future well, it is the one thing we do have influence over. In my earlier example, I can more easily influence the path of the avalanche than try to reverse it going down the hill, however, I can't predict exactly what the outcome will be even with my influence.

I said that with enough information, someone outside the universe could exactly predict the future, but one question arises: then what's the point if all the outcomes could be known by someone outside the universe? Indeed, this possibility of complete determinism seems to support all the believers in predestination. But if everything can be pre-determined, then what is the point of it actually playing out?

Look at simulations. When we run a simulation, it is like a little universe, and because of the code and the input, the outcome can be completely determined. So why do we run them if everything is known? Well, because even though we wrote the code and created the input, the process is too complex for us to predict the output directly. We can predict the output, but to do so requires running the simulation. I think this indicates the interesting possibility that whomever is running the show outside our universe is doing so because they don't know the outcome and are trying to find it out. They wrote the code (laws of the universe) and created the input (initial conditions), but have to run it to see what happens.

You said: "Look at simulations. When we run a simulation, it is like a little universe, and because of the code and the input, the outcome can be completely determined."

Look at your history of Chaos Theory. Simulations of weather were built with your stated assumption. However when the simulation was stopped and all the variables recorded then restarted with all those variables re-entered the outcome (given enough cycles) was radically different than if they had let the simulation continue to run. Very, very small changes in "initial conditions" propagate themselves over time to result in drastic changes. Hence the 'butterfly effect': A butterfly flapping its wings in India results in a hurricane in the Atlantic two years later.

Also, the great minds in physics found that below a certain level of measurement that the particles did not behave in a deterministic fashion.

It is not a question of how much information you gather, its a question of the inherent ambiguity of the Universe, itself. Weathermen are unable to accurately predict weather much past two weeks not because of a lack of information, but because the very nature of weather (and all of the universe) is just simply unpredictable.

I think the idea of blaming the lack of effectiveness of weather predictability on the inherent ambiguity of the universe is bunk. On the scale needed to predict the weather, it is only a matter of enough information and precision. People like to blame it on chaos or "unpredictability" rather than admitting they are not clever enough to really do it.

The old example of reloading the values of a weather sim as initial conditions causing radical differences over a long time is merely due to variable precision. If you put the exact binary values back to the complete precision they existed in the program, you would have the identical answer as if you had let the original simulation run on. So it in no way proves chaos theory.

From Wikipedia on Albert Einstien:

"In a 1926 letter to Max Born, Einstein made a remark that is now famous:

'Quantum mechanics is certainly imposing. But an inner voice tells me it is not yet the real thing. The theory says a lot, but does not really bring us any closer to the secret of the Old One. I, at any rate, am convinced that He does not throw dice.'

To this, Bohr, who sparred with Einstein on quantum theory, retorted, 'Stop telling God what He must do!' The Bohr-Einstein debates on foundational aspects of quantum mechanics happened during the Solvay Conferences."

Here are some relevant excerpts from http://www.hawking.org.uk/pdf/dice.pdf A lecture called "Does God play dice" given by Stephen Hawking:

The idea that the state of the universe at one time determines the state at all other times, has been a central tenet of science, ever since Laplace's time. It implies that we can predict the future, in principle at least.

In practice, however, our ability to predict the future is severely limited by the complexity of the equations, and the fact that they often have a property called chaos. As those who have seen Jurassic Park will know, this means a tiny disturbance in one place, can cause a major change in another. A butterfly flapping its wings can cause rain in Central Park, New York. The trouble is, it is not repeatable. The next time the butterfly flaps its wings, a host of other things will be different, which will also influence the weather. That is why weather forecasts are so unreliable.

Despite these practical difficulties, scientific determinism, remained the official dogma throughout the 19th century. However, in the 20th century, there have been two developments that show that Laplace's vision, of a complete prediction of the future, can not be realised.
first of these developments was what is called, quantum mechanics.
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It was some time before people realised the implications of this quantum behaviour for determinism.
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Einstein was very unhappy about this apparent randomness in nature. His views were summed up in his famous phrase, 'God does not play dice'. He seemed to have felt that the uncertainty was only provisional: but that there was an underlying reality, in which particles would have well defined positions and speeds, and would evolve according to deterministic laws, in the spirit of Laplace.
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Hidden variable theories might seem to be the most obvious way to incorporate the Uncertainty Principle into physics. They form the basis of the mental picture of the universe, held by many scientists, and almost all philosophers of science. But these hidden variable theories are wrong. The British physicist, John Bell, who died recently, devised an experimental test that would distinguish hidden variable theories. When the experiment was carried out carefully, the results were inconsistent with hidden variables. Thus it seems that even God is bound by the Uncertainty Principle, and can not know both the position, and the speed, of a particle. So God does play dice with the universe. All the evidence points to him being an inveterate gambler, who throws the dice on every possible occasion.

I think the idea that you can predict is still sound even considering underlying quantum mechanics. Quantum mechanics relies on probabilities but that doe snot mean nothing can be predicted. In facts it means predictions not dterminations are all you can do. But predictions very often turn out right especially as you get to the macro level. That's where all the little improbabilities start to cancel each other out and you see predictability. This doesn't disprove chaos theory but it also isn't an out for meteorologists either.

In other words, as we all know, the answer isn't simple.

I didn't mean to create a false delema.

Yes, the ability to predict still exists. The "larger" (less suseptable to quantum fluctuations) the item/event is the more accurate our prediction capability. Also, the shorter the time frame the more accurate the ability to predict.

However even for very large items/events the effect of chaos will make it difficult to predict its future state when there is enough time given.

Note: the 'failure' of scientific determinism does not prevent metaphysical prophecy. Let me explain. If prophecy works by altering the future instead of revealing what is predetermined, then it can still work in a non-deterministic existence.

As 'the Oracle' in The Matrix said "what is really going to bake your noodle later on is 'would you still have broken the vase if I hadn't said anything'?".

So, I draw a distinction between prediction (which decreases in accuracy given more time) and prophecy (which increases in accuracy given more time).

"our ability to predict the future is severely limited by the complexity of the equations, and the fact that they often have a property called chaos...this means a tiny disturbance in one place, can cause a major change in another."

None of that says randomness. It only appears random because your models are not good enough or that your models are too hard to evaluate. Again, it is just an excuse.

It is also not to say that you can't model these things with probability. I can model where the bullets will impact a target board using probability, and it might be pretty good, especially on average, but not exact for a particular shoot. However, to do any better means modeling the bullet trajectories, and to get the right answer, you have to take into acocunt more and more variables. It certainly gets complex, and you can call that complexity "chaos theory" if you like.

All chaos theory is means is that things are more complex than we tend to think. The weather simulation example illustrates this. The person running the simulation stops it, prints out the values of the variables, then re-keys them later to find out it was not the same as letting it play through. Well, that just illustrated that he forgot that he entered in rounded off values rather than the identical binary images and not that there was some dark mysterious "dice rolling" going on. Certainly, it did show that there are things that are sensitive to initial conditions. An easy example is a model for which side of a pyramid a ball will roll down. Certainly, it will be sensitive to very small differences in initial conditions to figure out which way the resultant force points - unless a strong prevailing wind is blowing, of course.

What you refer to as 'not knowing enough' Hawking refers to as 'hidden variable'. He states that experiments were done that show no hidden variable(s) exist.... that things behave 'as if' they are random because they are truly random.

Do you know more about physics than the man who wholds the seat at Cambridge that was once held by Newton?

So no hidden variables exist. All I said was that I observe that people who do things like predict the weather don't seem to bother to look at all of the variables - not that they were hidden.

People seem very fond of mentioning the chaos idea of a butterfly flapping its wings here causes some massive (always bad - never good because that's less dramatic) weather effect over there later. I'm just saying that is possible, but that I don't know of any weather models that are taking butterflies into account.

Until they do, they cannot throw up their hands and claim that weather is ''random''. Really they don't do that - they claim ''chaos'', which means it looks random because they are not taking everything into account. If they ever did take everything into account and weather still appeared random, then they could say it is random. I'm just pointing out the logic here, not disputing that there are truly random things in the universe.

If you accept that science is always right, then you get into dangerous ground.

All hawking is really explaining is the latest theory, but its already in trouble. String theory is challenging Quantum in some area's as there are places that quantum no longer works, and string theory is falling apart in other area's. Einstein explaned the realtionship between matter and energy with such prescision that we have the atomic age, but einstein could not explain the universe either.

I have heard many times how Gallileo was Science versus religion, but in fact the religion of the day was State controlled and molded to the scientific views of the Day. The battle was really One Science model against another. The same was true of Louis Pasteur who was a chemist and had to fight the doctors of his day.

Any time we automatically use a credential to destroy the possibility of debate we have a weakened debate and we assume we know it all. Such arrogance does no favour to science. In fact its the biggest problem we have getting people into science as they feel all the questions are answered, as they are always told this at high school. The fact is there is still so much we don't know that any time we make a definate statement we find our selves in trouble.

I am worried about a lot of quantum theory, not because I cant understand it, but because I do. The very basis that all events are unknowable and therefor chaotic suits some are an almost religous level of fervour. Everything is random and nothing is real. But in my field we find that there so called randomness is actually just a more complex interaction than we first considered. In fact we are starting to see that the so called random events are in fact more related to our lack of understanding. The more we repeat the condition, the more we see that there was no randomness at all.

I respect Dr Hawkings work. But I often feel his own opinions move too quickly into fact which in time we will find to be as accturate as Einsteins comment that "I for one" ... Its called an opinion.

For example in calculating the age of the universe I feel that gravity has been taked too lightly. Such an event would have an event horizon and thus there would be a time dilation effect. Yet hawking see's fit to dismiss it based not on Math, but on his opinion. It is not only possible that a big bang would create a universe with different ages within it, It is in fact almost certain that the effects of time dilation would mean that the universe has many different ages in it, and that may help xplain the missing first 3 seconds even better than the current quantum focus.

Either way. No-one knows it all, and we should remember that healthy debate means that we need to seriously consider new idea's sometimes they see something we are blinded to as we push our own work forward.

There is so much more to know, and we don't have anything close to enough information yet to state any more than the most basic of "Facts"

There is no quantum involved in this technique. (Which may be its downfall)

The only particle that travels at the speed of light is light otherwise it would have infinate mass (GR) so it is the injected particle.

The space swirl is pure newtonian physics based on the gravitational effects of moving particles upon the fabric of space.

The combined speed of the two particles is relative to the observer, and so the particle move backwards in time based on the observers experience as it tunnels back. The particle travels faster than light only to an observer outside the experiment. No laws of physics are broken, but they sure act as though they had been broken.

(at this point there is a risk that something else may happen at a quantum level, but so far no-one has been able to find out)

If this effect works then its possible that our views of cosmology may also be altered as the material pulled into a black hole may also experience the same effect and may in fact travel backward in time to the moment of creation ... The Supernova, where it would be released as energy in the instant of the nova. Maybe one day we can measure the mass and power of a nova and see if there is more energy than there should be, which would also be a way to explain why the universe is mathematically out of balance with Matter and energy.

It may still be conserved but not in the original time at which it changed form energy to matter or matter to energy.

If nothing else, Its a fascinating thought

Hope that makes sense, I'm fighting a head cold, so I may be less than clear right now.